1. Field of the Invention
The present invention relates to a peripheral device of a computer and more specifically to a RAID system which constitutes a storage system by combining a plurality of storage devices, and a data transfer method in the system.
2. Description of the Related Art
A RAID (Redundant Arrays of Inexpensive Disks) system is known to have several usage modes including one in which a plurality of storage devices having a relatively small memory capacity are combined to be used as a virtual single storage device having a large memory capacity (striping), and one in which the same data are recorded in a plurality of storage devices so as to back up the data (mirroring). Further, there are seven levels from RAID-0 to RAID-6 in terms of the method of parity processing, and the like.
The RAID system is broadly divided into two types based on the follow in methods; a method which utilizes special hardware (hardware-based method) and a method which is implemented by software (software-based method). Out of these, the hardware-based method includes two types: one which utilizes a RAID controller and one which utilizes a disk array unit.
Out of these, the RAID system which utilizes a RAID controller has a configuration in which a plurality of storage devices are connected in parallel to an integrated circuit (chip) called a RAID controller, and is implemented by an arrangement that the RAID controller controls the transfer of data to and from each storage device.
Conventional RAID systems (in particular, one constructed by using a storage device connected to IDE (Integrated Device Electronics) bus) are configured such that one IDE device is connected in parallel to one IDE bus, and a plurality of IDE buses are provided as needed.
On the other hand, storage devices have diversified in recent years, and there have been proposed not only conventional hard disk devices, but also a new memory device called a “silicon disk” which utilizes a semi-conductor memory device such as a flash memory. The basic features of the RAID system such as striping or mirroring, and enhancement of transfer rate can be carried over as they are even when the storage device is changed from a hard disk to a silicon disk. Particularly, a RAID system based on a striping method called a RAID-0 does not complement the redundancy of data, but has gained attention as the system to implement a high speed, large capacity memory device in place of hard disks by utilizing a plurality of memory cards having a small memory capacity (see for example, Japanese Patent Laid-Open No. 2000-207137).